Methods for selectively removing adhesives from polyimide substrates

Abstract

Methods for forming holes of predetermined size in polyimide substrates having metallic layers adhesively attached thereto include selectively removing areas of desired size and shape from the metallic layer; contacting the exposed adhesive layer with a selective etchant therefor that does not affect the polyimide substrate or undercut the adhesive near the opening formed; and selectively etching the polyimide substrate exposed in the openings by removal of the adhesive layer overlying the polyimides. These methods permit rapid, efficient formation of holes having a diameter as small as one mil (0.00254 cm).

What is claimed is: 
     
       1. A method for forming holes of predetermined size in a polyimide substrate having thereon a metallic layer and an adhesive layer linking said polyimide substrate to said metallic layer, said adhesive including a cross-linked acrylic polymer, comprising: (a) forming at least one opening in said metallic layer, exposing a portion of said adhesive layer;   (b) contacting the portion of said adhesive layer exposed in said at least one opening with an alkaline glycol solution at a temperature in the range of about 120° C. to about 145° C., and for a time sufficient to loosen said exposed portion of said adhesive layer, and then removing said exposed portion of said adhesive layer by contacting said exposed portion with an adhesive-removing medium; and   (c) contacting the portion of said polyimide substrate exposed by the removal of said portion of said adhesive layer, with an etchant for selectively removing exposed polyimide substrate from said at least one opening, said etchant being substantially non-reactive with said adhesive layer under the conditions of said contacting.   
     
     
       2. A method for forming at least one hole of predetermined size in a polyimide substrate having thereon an adhesive layer comprising a cross-linked acrylic polymer including: (a) forming at least one opening of said predetermined size in said adhesive layer by contacting a predetermined portion of said adhesive layer with a selective medium for said adhesive at a temperature in the range of about 120° C. to about 145° C., and for a time sufficient to loosen the predetermined portion of said adhesive, and then removing said predetermined portion of said adhesive layer by contacting said predetermined portion with an adhesive-removing medium, said time being insufficient to cause any substantial removal of said adhesive layer beyond the edges of said at least one opening; and   (b) contacting a predetermined portion of said polyimide substrate exposed by said at least one opening in said adhesive layer with an etchant for selectively removing said exposed polyimide substrate from said at least one opening, said etchant being substantially non-reactive with said adhesive layer under the conditions of said contacting.   
     
     
       3. The process of claim 1 wherein said etchant for selectively removing said polyimide substrate comprises hydrazine hydrate and a diamine. 
     
     
       4. The process of claim 3 wherein said diamine is ethylene diamine. 
     
     
       5. The process of claim 1 further comprising contacting said exposed adhesive layer in said at least one opening at a temperature of about 120° C. for a time in the range of about 30 to about 180 seconds. 
     
     
       6. The process of claim 1 wherein said holes of predetermied size are at least about one mil (0.00254 cm) in diameter. 
     
     
       7. The process of claim 1 wherein said polyimide is Kapton. 
     
     
       8. The process of claim 1 wherein said metallic layer comprises copper cladding. 
     
     
       9. The process of claim 1 wherein the ratio of the combined thicknesses of said polyimide substrate, said metallic layer and said adhesive layer, to the diameter of said at least one hole of predetermined size is in the range of less than 0.5 to about 1. 
     
     
       10. The process of claim 1 further comprising after said contacting with said etchant for selectively removing said polyimide, honing said at least one hole for a time sufficient to remove substantially all of the uneven edges from the surfaces thereof. 
     
     
       11. A method for removing adhesive material comprising a cross-linked acrylic polymer from an area of predetermined size on the surface of a polyimide substrate comprising contacting said area with a selective etchant for said adhesive comprising an alkaline glycol solution at a temperature in the range of about 120° C. to about 145° C., and for a time sufficient to loosen said area from said polyimide substrate without substantial damage to any other area on said surface, and then removing said exposed portion of said adhesive layer by contacting said exposed portion with an adhesive-removing medium. 
     
     
       12. The method of claim 1 wherein said polyimide substrate has a first said metallic layer and a first said adhesive layer on a first side of said substrate and a second said metallic layer and a second said adhesive layer on a second side of said substrate opposing said first side. 
     
     
       13. The method of claim 12 wherein at least one of said holes is a blind hole. 
     
     
       14. The method of claim 12 wherein at least one of said holes is a through hole, and wherein said through hole is made by forming in each of said first and second metallic layers at least one opening in registration with one another on opposing sides of said polyimide substrate, and wherein the portions of said first and second adhesive layers exposed in each of said openings, and the portions of said polyimide substrate between said openings, are removed.